Installation of a lens into a high precision lens assembly, particularly nontraditional lens assemblies such as those that may be used in thermal imaging cameras and other cameras, requires a time consuming and costly alignment process to assure precise positioning of the lens. For example, the lens must not only have its optical axis aligned but must also be parallel to the cell in which it is mounted and have no tilt. If multiple lenses are used, the optical axis of all lenses must be precisely aligned and they must each be parallel to each other. Any errors in alignment will negatively impact the images produced by the lenses. In order to achieve this precise lens placement, the components holding the lens must be manufactured with extremely tight tolerances. For example, if a bore is used to mount the lens, it must be manufactured with very tight tolerances with regard to multiple factors including true position, circularity and concentricity. In addition, highly qualified surfaces are traditionally required to attain proper lens placement, which result in further expense. More sophisticated methods still require a perfectly qualified lens shelf. The manufacture of the component pieces, including the mounts and the lenses to such high tolerances is expensive, as is the time consuming process of mounting the lens.
In some systems, high precision lens mounting can be achieved when mounting a lens through the use of high tolerances in the manufacture of the components and the use of qualified lenses. However, the use of such high tolerances is very expensive, making it too expensive for some applications.
For lens assemblies with lower tolerances, one method of mounting high precision lenses into a lens cell includes the use of sets of gauged pins having sizes that vary in small increments. The lens is placed into the lens cell, then a first set of pins of equal diameter is placed into the gap between the edge of the lens and the inside wall of the lens cell. For example, three pins may be placed into the gap, spaced apart around the lens. If the fit is too loose, the pins are removed and replaced with another set of pins having a slightly larger diameter. If the fit is too tight, the pins are removed and replaced with another set having a slightly smaller circumference. The process is repeated until the desired snug fit of the pins is achieved. In this way, the lens is stabilized in a centered location in the lens cell. The lens can then be adhered to the cell and the pins can be removed. This iterative process is performed manually, requiring a large amount of time and expense.
Another method of mounting high precision lenses uses an optical alignment system. In this method, the lens is mounted on an air bearing spindle and is gently nudged into alignment. For example, the operator may nudge the edge of the lens using a cotton swab to attempt to center the lens. The alignment of the lens is determined using an autocollimator, which passes a laser beam through the lens or is reflected off the lens while it rotates on the air bearing spindle. The operator must observe the transmitted or reflected laser light beam for wobbling, which indicates a decentered position of the spinning lens, to determine if the lens is properly centered, and must adjust the lens by manually nudging it back and forth until the proper alignment is achieved as indicated by observation of the laser beams. High tolerances can be achieved by this method, but it is laborious and time consuming. This taxing process to mount one lens may take between 15 minutes and one hour, for example, resulting in considerable operator fatigue.
Because of the existing processes for mounting lenses are time consuming and difficult, alternative processes which are quicker and simpler are desired.